1. Field of Invention
The present invention relates to a source driver. More particularly, the present invention relates to a digital-to-analog converter of a source driver.
2. Description of Related Art
FIG. 1 shows a function block of a digital-to-analog converter (DAC) of a LCD source driver. Output voltage Vout is selected with a switch array 108 from gamma voltages Vr0˜Vr2−1n from a corresponding decoder input which is controlled by digital codes A0˜An−1. Here, An−1 is chosen as Most Significant Bit (MSB) and A0 is chosen as Least Significant Bit (LSB).
For a conventional line-inversion LCD, the switch array 108 as illustrated in FIG. 2 requires two full sets of columns 118 and 128, which have different transistor types for the two groups of gamma voltages provided in response to different polarities while the line-inversion LCD displaying, respectively, one set of the columns 118 having P-type Metal-Oxide-Semiconductor (PMOS) transistors and the other set of the columns 128 having N-type Metal-Oxide-Semiconductor (NMOS) transistors, and therefore this architecture occupies large area of the source driver chip.